Apparatus for reaming a patella

ABSTRACT

An apparatus for reaming a patella includes a clamp for securing the patella and a reamer. The reamer includes a depth scale to indicate a depth to which the patella has been reamed. The clamp includes a pivoting collet to enable the clamp to stably secure different patellas having a variety of shapes and sizes. The stability of the collet is ensured by a plurality of prongs on the side contacting the patella, which are arranged to be equally spaced around the peak of the patella. Using this reaming apparatus, the depth to which the patella is reamed can be accurately determined. The reamed patella can then be fitted with a prosthesis to coordinate with a femoral prosthesis fitted on a resected femur and a tibial prosthesis fitted on a resected proximal end of a tibia to form a reconstructed knee joint which is substantially at anatomic level and has a proper degree of laxity in both flexion and extension.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application to U.S. patent applicationSer. No. 09/177,334, filed Oct. 22, 1998, entitled METHOD AND APPARATUSFOR LOCATING BONE CUTS AT THE DISTAL CONDYLAR FEMUR REGION TO RECEIVE AFEMORAL PROSTHESIS AND TO COORDINATE TIBIAL AND PATELLAR RESECTION ANDREPLACEMENT WITH FEMORAL RESECTION AND REPLACEMENT, now U.S. Pat. No.6,077,270 which is a continuation-in-part application to U.S. patentapplication Ser. No. 09/049,781, filed Mar. 27, 1998 entitled METHOD ANDAPPARATUS FOR LOCATING BONE CUTS AT THE DISTAL FEMORAL CONDYLES TORECEIVE A FEMORAL PROTHESIS AND TO COORDINATE TIBIAL AND PATELLARRESECTION AND REPLACEMENT WITH FEMORAL RESECTION AND REPLACEMENT, nowU.S. Pat. No. 6,024,746, which is a continuation-in-part application toU.S. patent application Ser. No. 08/956,015, filed Oct. 22, 1997entitled METHOD AND APPARATUS FOR LOCATING BONE CUTS AT THE DISTALCONDYLAR FEMUR REGION TO RECEIVE A FEMORAL PROTHESIS AND PROPERLYARTICULATED WITH PATELLAR AND TIBIAL PROTHESIS, now U.S. Pat. No.6,059,788, which is a continuation-in-part application to U.S. patentapplication Ser. No. 08/455,985, filed May 31, 1995, entitled METHOD ANDAPPARATUS FOR LOCATING BONE CUTS AT THE DISTAL CONDYLAR FEMUR REGION TORECEIVE A FEMORAL PROSTHESIS, now U.S. Pat. No. 5,776,137, issued Jul.7, 1998, the disclosures of which are incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to methods and apparatus for locating bone cuts onthe medial and lateral femoral condyles to form seating surfaces for afemoral knee prosthesis, and to coordinate tibial and patellar resectionand replacement with femoral resection and replacement.

The invention further relates to a tool for locating said cuts.

BACKGROUND OF THE INVENTION

Over the years, the concepts of designs for the total knee arthroplastyhave evolved to the point where with few exceptions, most are quitecomparable in the design of femoral, tibial and patellar prostheses.

Major discrepancies and problems encountered are caused by physicianerror and failure to understand the principles of more complex alignmentor ligament problems to be corrected at surgery. With the more complexalignment or “routine” degenerative knee, the major differences are theease and consistency of instrumentation for alignment and proper bonecuts allowing proper ligament balance. This allows satisfactory motionand stability post operatively.

The distal femoral cuts must be placed to provide the knee prosthesiswith a proper flexion and extension gap, proper varus-valgus alignment,proper patellofemoral relationship and proper rotation. It is customaryto use an intramedullary rod placed in a retrograde fashion between themedial and lateral femoral condyles just anterior to the intercondylarnotch to establish a single point of reference for subsequent bone cuts.A major problem is in the instrumentation to indicate the location ofthe femoral cuts which relies upon the “experience” or “eyeballing” ofthe surgeon. Over the years, two basic instrument system designs havebecome popular.

In one design (anterior referencing), the total knee alignment systemtakes its point of reference from a centrally placed rod and carefulattention is given to the patellofemoral joint by using an anteriorlyplaced feeler gage. The distal femoral cut is consistent with thethickness of the prosthesis.

This instrument system operates on the principle of anatomic anteriorand distal femoral cuts to allow proper ligament balancing and stabilityin extension as well as consistent patellofemoral placement on theanterior surface. The femur is not notched, and the anterior surface ofthe femoral prosthesis not elevated above the anterior surface of thefemur. Notching the femur may cause a decrease in strength of the distalfemur. Elevation of the anterior surface of the prosthesis will causeextremely high patellofemoral pressures in a joint that seems to beprone to a high rate of post-operative failure.

By establishing the anterior femoral cut as the benchmark or datumstarting point, however, the anterior referencing instruments result inthe installation of a knee prosthesis which sacrifices consistentstability in flexion due to the formation of a posterior femoralcondylar cut that may leave the posterior space either too wide or toonarrow. This can cause instability in flexion, or restrict flexion andcause increased wear.

The second type of instrument design (posterior referencing) is based onthe concept that the flexion and extension stability are more importantand the patellofemoral joint is of secondary importance. This systemalso uses an intramedullary rod for referencing. Although I consider allthree joints as “important”, when a compromise must be made, theposterior referencing systems compromise the patellofemoral joint whilethe anterior reference systems sacrifice stability in flexion (theposterior tibial femoral joint). Both systems allegedly equally addressthe distal tibial-femoral space. Neither consistently addresses thedistal rotation of the femoral component.

Neither system tries to preserve the joint line at or near an “anatomic”level. By elevating the jointline, the patella is distalized. The femuris also shortened. Since the arthritic knee often has a loss ofcartilage, there may be a patella infera of 2-3 mm initially. Elevatingthe distal femoral resection beyond this will:

1) Further alter the patellofemoral relationship.

2) Change the isometric and rotational balance of the MCL and the LCL.

3) Shorten the femur in flexion and may cause increased roll back,anterior lift off, and increased posteromedial wear.

4) Elevate the level of tibial resection necessitating a major amount ofposterior femoral resection to achieve a satisfactory flexion space.

When performing a unicompartmental knee replacement, it is imperative tomaintain the jointline. As a consequence, it is desirable to maintain afull range of motion.

SUMMARY OF THE INVENTION

An object of the invention is to provide methods and apparatus forlocating bone cuts on the medial and lateral femoral condyles to formseating surfaces for a femoral knee prosthesis, and to coordinate tibialand patellar resection and replacement with femoral resection andreplacement which reliably and anatomically provide:

1. Consistent distal tibio-femoral stability.

2. Consistent distal femoral rotation.

3. Consistent placement of the anterior cut flush with the anteriorsurface of the femoral cortex, i.e., without notching or elevation.

4. Consistent placement of the posterior femoral cut such that thedistal and posterior cuts are equal (when indicated) allowing forsatisfactory extension and flexion stability and motion.

The method and apparatus of the invention contemplate placement of theanatomic joint line which, in extreme cases, varies up to the differencebetween the anterior-posterior A-P internal measurements of the sizeprostheses. Based on my knowledge of total knee replacement, personalexperience with numerous routine total knee replacements, numerous morecomplicated cases consisting of knees with flexion deformities andrevision surgery, a maximum of a few mm proximal or distal displacementof the joint line is considerably less harmful than:

1. A lax flexion gap;

2. Sloping the proximal tibial cut to accommodate for an inconsistentposterior femoral condylar cut;

3. Significantly notching the femur anteriorly;

4. Raising the anterior flanges of the prosthesis and thus thepatellofemoral joint;

5. Not allowing full extension;

6. Raising the joint line;

7. Tightness in flexion;

8. Malrotation; and

9. Patient pain.

With an understanding of the measurements involved in total kneereplacement, a new instrument system and methodology has been developedto allow flexion 120-130 degrees; to perform less soft tissue releasing;and decrease surgical time. Starting with a “normal” knee, the goalshould be to maintain the anatomic landmarks as close to normal aspossible. Then, if deformities are present, the procedure can bemodified to accommodate the situation.

In accordance with the invention, a method is provided for formingplanar cuts on the medial and lateral condyles of the femur to formseating surfaces to receive a femoral knee prosthesis, comprising:

determining a prospective planar cut at the posterior of the condyles ofthe femur at which the distance between the anterior surface of thefemoral cortex and the prospective planar cuts is substantially equal tothe interior dimension of a knee prosthesis to be fitted on said femurat the anterior surface and the cut planar surface,

determining the thickness of the posterior lateral or medial condylewhich will be resected by said prospective planar cut,

cutting the distal ends of the condyles along a plane at which themaximum thickness of resection of the more prominent condyle at saiddistal end is substantially equal to the thickness determined to beresected at the posterior medial or lateral condyle by said prospectiveplanar cut, and

cutting the condyles along a plane substantially flush with the anteriorsurface of the femoral cortex, and along said prospective planar cut.

The method further contemplates loosely placing a longitudinalintramedullary rod in the femur such that an end of the rod projectsfrom the femur, mounting a tool on the projecting end of the rod,establishing, by said tool, an angular position of said prospectiveplanar cut along a plane rotated at an angle of between 0 and 15° withrespect to a tangential plane at the posterior of the lateral and medialcondyles about an axis located in said tangential plane.

In further accordance with the method, the tool is rotated with said rodthrough said angle and a datum or benchmark is established by therotated rod or by pins installed in the condyles on the basis of therotated position of the tool. A cutting guide can be mounted on saidtool, to enable the distal end of the condyles to be cut along saidplane. Thereafter, the tool is removed and a second A-P cutting guide ismounted on the selected benchmark, i.e., the rod or the pins and theposterior and anterior cuts are made. The axis about which the plane ofthe prospective cut is rotated is located in said tangential plane atthe posterior surfaces of the medial and lateral condyles and can belocated at either of the condyles or at any location therebetween. It isa feature of the invention that the tool may remain on the rod both forthe measurements and for the cutting of the distal end of the femur.

The invention also contemplates that the cutting guide supports a meanswhich enables the cutting guide to be secured to the condyles during thecutting of the distal ends of the condyles.

The invention further contemplates an apparatus for forming planarresections on the medial and lateral condyles of a femur to form seatingsurfaces to receive a femoral prosthesis and to properly articulate witha tibial and patellar prosthesis comprising:

a caliper feeler and measurement plate to measure for the size of thefemoral prosthesis to be received, said caliper feeler and measurementplate adapted to determine a first distance between an anterior surfaceof the femoral cortex and a plane tangent to a posterior surface of themedial and lateral condyles of a femur, the caliper feeler referencingthe anterior surface of the femoral cortex and the measurement platereferencing the plane tangent to the posterior surface of the medial andlateral condyles;

a graduated scale to compare the first distance to at least two standardfemoral prosthesis sizes and to determine the smaller of the at leasttwo standard femoral prosthesis sizes;

a graduated scale to measure a second distance between the firstdistance and the size of the smaller standard femoral prosthesis size,so that a thickness or thicknesses can be measured to be resected at theposterior surface of the medial and lateral condyles of the femur byadding the average thickness of the posterior condyles of the smallerstandard femoral prosthesis and the second distance;

a tool to resect the medial and lateral condyles along a plane at theanterior surfaces thereof flush with the anterior surface of the femoralcortex; and

a tool to resect distal ends of the medial and lateral condyles at aresected thickness equal to the average thickness of the distal condylesof the smaller standard femoral prosthesis plus the second distance.

The apparatus further contemplates a tool to resect the measuredthickness at the posterior surface of the medial and lateral condyles ofthe femur.

The invention also contemplates a method for forming planar resectionson the medial and lateral condyles of a femur to form seating surfacesto receive a femoral prosthesis and to properly articulate with a tibialand patellar prosthesis comprises:

measuring for the size of the femoral prosthesis to be received bydetermining a first distance between an anterior surface of the femoralcortex and a plane tangent to a posterior surface of the medial andlateral condyles of a femur;

using a graduated scale to compare the first distance to at least twostandard femoral prosthesis sizes;

measuring a second distance between the first distance and the size ofthe smaller standard femoral prosthesis size; and

measuring a thickness or thicknesses to be resected at the posteriorsurface of the medial and lateral condyles of the femur, the thicknessbeing equal to the average thickness of the posterior condyles of thesmaller standard femoral prosthesis plus the second distance.

The method further contemplates the steps of resecting the medial andlateral condyles along a plane at the anterior surfaces thereofsubstantially flush with the anterior surface of the femoral cortex; and

measuring a thickness or thicknesses to be resected at the distal endsof the medial and lateral condyles, the thickness being equal to theaverage thickness of the distal surface of the smaller standard femoralprosthesis plus the second distance, and resecting the distal ends ofthe medial and lateral condyles at the measured thickness.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic, lateral view of the femur and tibia at a kneejoint showing prospective cuts to be made on the femur for installationof a femoral prosthesis.

FIG. 2 is a diagrammatic illustration of the knee joint of FIG. 1 seenanteriorly of the joint.

FIG. 3 is an end view from the distal end of the femur of the kneejoint.

FIG. 4 is a sectional view of a femoral knee prosthesis adapted forplacement on the femur after the planar cuts have been made on thefemur.

FIG. 4a is a side view identifying each of the cuts made to the femur.

FIG. 5 is a side view similar to FIG. 1 in which the tibia has beenturned 90° to expose the distal end of the femur, an intramedullary rodhas been inserted into the femur and a tool placed on the rod, the toolbeing partly broken away and shown in section.

FIG. 6 is an end view of the tool taken in the direction of arrow 6—6 inFIG. 5.

FIG. 7 is a sectional view taken on line 7—7 in FIG. 6.

FIG. 8 is a broken, perspective view of a lower caliper feeler of thetool.

FIG. 9 is similar to FIG. 6 and illustrates a first stage in which therod is angularly rotated by a specific amount.

FIG. 10 is similar to FIG. 9 in a subsequent stage.

FIG. 11 is an exploded view showing a cutting guide to be installed onthe tool.

FIG. 12 is a top, plan view showing the cutting guide installed on thetool.

FIG. 13 illustrates the distal end of the femur after the distal end hasbeen cut and an AP cutting guide has been placed on the rod.

FIG. 14 is an end view similar to FIG. 6 of a second embodiment of thetool.

FIG. 15 shows the tool of FIG. 14 in a rotated state.

FIG. 16 is an end view similar to FIG. 6 of a third embodiment of thetool.

FIG. 17 shows the tool of FIG. 16 in a rotated state.

FIG. 18 is an end view similar to FIG. 6 of a fourth embodiment of thetool.

FIG. 19 shows the tool of FIG. 18 in a rotated state.

FIG. 20 is similar to FIG. 13 but shows a modification adapted to theembodiment of FIGS. 16 and 17.

FIG. 21 is an end view similar to FIG. 6 of a fifth embodiment of thetool including an A-P measuring guide.

FIG. 22 is a side view similar to FIG. 5 of the tool of FIG. 21 mountedon the distal femur.

FIG. 23 is a top view of the tool of FIG. 21 mounted on the distalfemur.

FIG. 24 is an exploded view of a distal cutting block to be installed onthe tool of FIG. 21.

FIG. 25 is a side view of the tool of FIG. 21 mounted on the femurinstalled with the distal cutting block.

FIG. 26 is a top view of the tool of FIG. 25 mounted on the femur.

FIG. 27 is an enlarged fragmentary view of the sliding scale of thedistal cutting block.

FIG. 28 is a side view of the femur with the distal cutting blockmounted thereon.

FIG. 29 is a top view of the A-P cutting block mounted on the distalfemur.

FIG. 30 is a view similar to FIG. 13 illustrating the distal end of thefemur after the distal end has been cut and the A-P cutting block hasbeen mounted thereon.

FIG. 31 is a top view of the A-P cutting block mounted on the distal endof the femur after the distal end has been cut and the A-P cutting blockhas been mounted thereon.

FIG. 32 is a side view of the distal end of a femur after it has beencut and a preferred prosthesis is ready to be mounted thereon.

FIG. 33 is a front view of the preferred prosthesis to be used with thetool of FIG. 21.

FIG. 34 is an alternative embodiment of the tool of FIG. 22, includingposterior clips.

FIG. 34a is a rear perspective view of a posterior clip of FIG. 34.

FIG. 34b is a front perspective view of a posterior clip of FIG. 34.

FIG. 35 is a top view of the tool of FIG. 34.

FIG. 36 is a front view of the tool of FIG. 34.

FIG. 37 is rear view of the tool of FIG. 34.

FIG. 38 is a top view of the tool of FIG. 34 mounted on the femurinstalled with a distal femoral cutting block and a distal femoralresection caliper.

FIG. 39 is a top view of the femur with the distal femoral cutting blockmounted thereon.

FIGS. 40 and 41 are perspective views of distal femoral resectioncalipers for use in right and left femurs.

FIG. 42 is a front view of a tibial resection guide of the presentinvention mounted on a tibia.

FIG. 43 is a side view of the tibial resection guide of FIG. 42.

FIG. 44 is a top view of the tibial resection guide of FIG. 42.

FIG. 45 is a side view of a tibial external resection guide of thepresent invention mounted on a tibia.

FIG. 46 is a top view of a spacer of the present invention.

FIG. 46a is an end view of the top extension portion of the spacer ofFIG. 46.

FIG. 46b is an end view of the bottom flexion top extension portion ofthe spacer of FIG. 46.

FIG. 47 is a side view of the spacer of FIG. 46.

FIG. 48 is a front view of the knee space including a spacer in flexion.

FIG. 49 is a front view of the knee space including a spacer inextension.

FIG. 50 is a side view of a tibial reresection guide in accordance withthe present invention mounted on a tibia.

FIG. 51 is a front view of the tibial reresection guide of FIG. 50.

FIG. 52 is a top view of a tibial reresection guide of FIG. 50.

FIG. 53 is a partial side view of a patellar clamp including a hingefeature in accordance with the present invention.

FIG. 53a is a partial top view of the hinge feature of the patellarclamp of FIG. 53.

FIG. 54 is an end view of the patellar clamp of FIG. 53 showing a scaleto measure the patella thickness.

FIG. 55 is a side view of a patellar clamp in accordance with thepresent invention without the hinge feature shown reaming a patella.

FIG. 56 is a top view of the patellar clamp of FIG. 55 reaming apatella.

FIG. 57 is a side partially broken away view of a patella having apatella insert fitted therein.

FIG. 58 is a side view of an improved nail in accordance with thepresent invention.

FIG. 59 is a side view of the tool of FIG. 34 mounted on a femurinstalled with a distal femoral cutting block and a distal femoralresection caliper of the present invention, showing the nail of FIG. 58being removed from the femur in accordance with an improved slap hammerof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

When performing a unicompartmental knee replacement, it is imperative tomaintain the jointline at or near anatomic level. As a consequence, thismaintains a full range of motion. The instrument system of the presentinvention has been developed which combines the advantages of anteriorand posterior referencing systems to maximize motion in a reproduciblefashion and can easily be incorporated into an operative protocol. Withthe instrument system of the present invention, orthopedic surgeons canreconstruct a knee and retain “anatomic” landmarks. This makes itpossible to deal with many of the deformities confronting the orthopedicsurgeon in an arthritic knee.

There are three ways that joint surgeons can insert a total kneereplacement:

1) Resect the distal femur to accommodate the thickness of the femoralprosthesis. Resect the proximal tibia to accommodate the thickness ofthe tibial prosthesis. This recreates any lost motion and requires majorsoft tissue releasing. The flexion and extension resection spaces arenot coordinated.

2) Rebuild the “normal” knee by compensating for loss articularcartilage and bone in the measurements for bony resection; then softtissue releases can be performed to accommodate the proper dimensions.This places even greater demands on contracted soft tissues. Althoughthis may be most anatomically correct, it requires such major tissuereleases as to make it impractical.

3) Accept bony and articular cartilage loss. Resect the amount of bonein flexion and extension to accommodate full extension and as muchflexion as deemed necessary. This method relies on a coordinatedresection of the flexion-extension spacing. It relies on accuratemeasurements to allow for the resection of bone and minor soft tissuerelease. Within certain parameters, this method is preferable and canonly be possible with better instrumentation, such as theinstrumentation of the present invention.

Referring now to FIG. 1, the drawing diagrammatically illustrates thefemur 1 and tibia 2 of a knee joint 3. The invention is concerned withthe placement of planar resections or cuts at the distal condylar region4 of the femur 1 to receive a femoral knee prosthesis 5 (FIG. 4).Typically, a total knee replacement also requires placing a planar cutat the proximal tibia of the tibia 2 to receive a tibial prosthesis, notshown. The tibial prosthesis typically consists of a tibial baseplate,not shown, that is fitted on the proximal tibia after the tibial cut ismade, and an articular insert, not shown, secured to the baseplate toarticulate with the femoral prosthesis 5.

The cut made on the tibia 2 and installation of the tibial kneeprosthesis should be as close to the anatomic level as possible andshould be substantially parallel to the floor in the mediolateral plane.This maintains the joint line at or close to anatomic level. Moreover,the angle of the proximal tibial resection should correspond to theangle of the distal femoral resections 12. For example, the proximaltibia is in mild varus and is resected such that the resection in themediolateral plane is parallel to the floor and oriented posteriorlyabout 3°. Accordingly, the cuts made on the femoral prosthesis,discussed below, must also take into account this 3° mediolateralorientation in order to align the femoral prosthesis with the tibialprosthesis as will be explained later.

Assuming normal anatomy, it is also important that the resected spacemedially in extension between the tibia 2 and the femur 1 of the kneeequals the combined thickness of the medial tibial prosthesis and thedistal medial femoral prosthesis; that the resected space laterally inextension between the tibia 2 and the femur 1 of the knee equals thecombined thickness of the lateral tibial prosthesis and the distallateral femoral prosthesis; that the resected space medially in flexionbetween the tibia 2 and the femur 1 of the knee equals the combinedthickness of the medial tibial prosthesis and the posterior medialfemoral prosthesis; that the resected space laterally in flexion betweenthe tibia 2 and the femur 1 of the knee equals the combined thickness ofthe lateral tibial prosthesis and the posterior lateral femoralprosthesis; and that the resected space between the tibia 2 and thefemur 1 of the knee in flexion must be equal to or greater than theresected space between the tibia 2 and the femur 1 of the knee laterallyin extension, assuming normal ligament balance.

The condylar region 4 of the femur 1 is formed with a medial condyle 6and a lateral condyle 7 separated by an intercondylar notch 8. The femur1 includes a shaft 9 forming the femoral cortex, the condylar region 4being at the distal end of the shaft 9.

In order to install the femoral knee prosthesis 5 on the distal condylarregion 4 of the femur 1, three planar cuts are made in the condylarregion 4 to form seating surfaces for the prosthesis 5. These cutsconsist of an anterior cut 10, a posterior cut 11 and a distal end cut12. The placement of these cuts 10, 11, 12 is crucial to theinstallation of the prosthesis 5 and its effect on the overall functionof the prosthetic knee joint.

The invention is based on complying with the following conditions.

1. Forming the planar cut 10 at the anterior surface of the femoralcondylar region flush with the anterior surface 13 of the femoral cortexso as to form a continuous surface therewith free of formation of eithera notch or elevation at the juncture of cut 10 and surface 13.

2. Forming the planar cut 11 at the posterior surface of the femoralcondylar region at a distance D from planar cut 10 equal to the interiordimension S between the anterior and posterior mounting surfaces 14, 15of the prosthesis 5. The dimension S is the so-called A-P distance ofthe prosthesis and this distance varies for different size prostheses.For example, prosthesis are categorized as small, small(+), medium,large, large(+) and extra large and the A-P distance increases inproportion to the size increase.

With reference to FIG. 3, therein is seen a plane T tangential to themedial and lateral condyles at the posterior surface 16 of the condylarregion. The planar cut 11 is made at an angle A, with respect to plane Tto angularly align the femoral prosthesis with the tibial prosthesis.Normally, the angle would be 3° to match the angle of the tibialprosthesis, however, due to anatomical conditions of the patient such aswear of the medial or lateral condyles posteriorly the angle A can varysubstantially, generally between 0 and 15°. The planar cut 11 willresult in resection of bone of a thickness t₁ at the medial condyle 6and a thickness t₃ at the lateral condyle. The thickness t₃ is usuallyless than t₁ and controls the location of planar cut 11 so that aminimum thickness of bone is resected at the posterior surfaces of thecondyles. In this regard, the thickness t₃ is established as thedifference between distance D′ between the anterior surface 13 of thefemoral cortex and a plane P tangent to the posterior surface of thelateral condyle 7 and parallel to planar cut 11 and distance D betweenthe anterior surface of the femoral cortex 13 and planar cut 11.

The thickness t₃ and the location of the prospective planar cut 11therefore can be established based on measurement of the distance D andthe A/P dimension of the selected size of the prosthesis. The size ofthe prosthesis is determined on the basis of the measurement of thedistance D′ and in general, the prosthesis size will be selected so thatthe thickness t₃ falls within a relatively narrow range, generally atleast 6 mm and between 6 and 11 mm. The resected thickness of bone t₁and t₃ at the medial and lateral condyles are generally unequal.

The distal end cut 12 is made so that the maximum thickness t₂ of boneresected at the distal end is substantially equal to t₃, i.e., themaximum thickness t₂ of bone resected at the more prominent condyle atthe distal end (the medial condyle 6 in FIG. 2) is equal to the minimumthickness t₃ of bone resected at the posterior surface.

Referring now to FIG. 5, in order to establish the precise positions ofthe three planar cuts 10, 11, 12 to be made on the femur 1, areferencing or datum system is utilized which in the description hereinis in the form of an intramedullary rod 20 installed in a bore 21 formedin the femur 1. The use of the intramedullary rod 20 as a benchmark ordatum is known in the art and is illustrated herein by way of example.Other referencing or datum systems can be employed as well, for example,utilizing two pins placed in the condyles as set distance below theanterior femoral cut to position an AP cutting guide thereon. This willbe described later.

The bore 21, which is approximately 8 mm in diameter, is formedlongitudinally in the shaft 9 and in the condylar region 4 of the femur1 at a location which is slightly anterior and medial of theintercondylar notch 8. The rod 20 has a cylindrical portion 22 whichsnugly fits in the bore 21 but is able to be rotated in the bore 21. Therod 20 may include radial flutes 23 extending outwardly a distanceslightly greater than the diameter of the bore 21. The flutes 23 areinitially outside the bore 21 and are intended to be driven into thebore 21 to fixedly secure the rod 20 in the bore 21. For this purpose,the flutes 23 are tapered to facilitate driving them into the bore 21and grip the bore tightly in the distal femur 1 when driven therein. Theouter ends of the flutes 23 can be saw-tooth or jagged as shown in FIG.7 to provide a resilient gripping action.

The rod 20 includes an adjunct end or stub 24 which is non-circular incross-section. The stub 24 may extend at an angle with respect to thelongitudinal axis of the rest of the shaft so as to be substantiallyperpendicular to the joint and the prospective distal end cut 12 andparallel to the weight bearing mechanical axis of the leg. Shafts havingstubs with different angles varying about 5-7° may be provided andselection is made on the sex, anatomical condition, and other conditionsof the patient. This is conventional in prior usage.

The angular position of the non-circular stub 24 in bore 21 when theflutes 23 are driven into the bore 21 is a measure of the angle A atwhich the posterior and anterior cuts 11, 10 are made and, consequently,of the angular position of the knee prosthesis 5 on the femur 1 relativeto the weight bearing mechanical axis of the leg.

The anatomical conditions governing the angular position of the rod 20in the bore 21 is based on anatomy to maintain a straight line betweenthe hip joint or the center of the femoral head in neutral rotation, thecenter of the knee joint and the midmedial third of the tibial plafond.

If the rod 20 initially assumes an angular position parallel to plane T,the rod is rotated by angle A to reach its datum position from which thecuts 10, 11, 12 will eventually be made. Nominally, the rotation is atan angle 3° to match the angle of the tibia prosthesis. However, due towear of the condyles, and anatomical conditions of the patient therotation of the rod must be varied from 3° to match the tibiaprosthesis. The surgeon is readily able to estimate this angle based onthe anatomy and on X-rays of the patient. Heretofore, however, thesurgeon had to estimate the angle at which to set the rod 20 when therod is driven into the bore 21. An imprecise estimate of the rotationalorientation of the stub 24 can lead to angulation and placement errorsof the prosthesis. Stated succinctly, the estimate of the surgeon of theangulation of cut 11 based on patient anatomy is accurate, but the“eyeballing” of the rotational position of the stub is often inaccurate.

The invention provides a tool or instrument 30 which is fitted on thestub 24 of rod 20 and accurately establishes rotation of the rod 20 whenit is driven into the bore 21 and which measures the distance D′ whichin turn will determine the location of the planar cuts 10, 11, 12.

The tool 30 includes a sleeve 31 having a circular-like bore 32 of thesame shape as the stub 24 in order to be fitted on the stub 24 forcommon rotation therewith. The bore 32 should include longitudinal slotsor striations, e.g., star-shaped. The sleeve 31 has grooves 33 alignedwith flutes 23 to permit passage of the flutes 23 through the sleeve 31when the rod 20 is driven into the bore 21 in the shaft 9 of the femur1. The sleeve 31 is rotatably supported in a slider 34 which is slidablysupported by a lower half 35 of a caliper means whose upper half 36 isslidably engaged with lower half 35. The upper and lower halves 36, 35are formed as open U-shaped members forming adjacent legs 37, 38 whichare slidably engaged by tongue and groove engagement means 39. Theslider 34 is slidably engaged in the legs 37 of the lower half 35 of thecaliper means by a tongue and groove engagement means 40.

A cross leg 41 at the closed end of the lower half 35 of the calipermeans engages a bar 42 for slidable movement in a directionsubstantially perpendicular to the direction of slidable movement ofslider 34. The bar 42 is formed with opposed flats 43 on which the crossleg 41 can slide without undergoing rotation. The bar 42 is providedwith forwardly facing pins 44 at end regions thereof.

A posterior caliper 45 is mounted on the pins 44. The posterior caliper45 includes a caliper plate 46 with spaced caliper feelers 47 (FIG. 8)for respectively contacting the posterior surfaces of the medial andlateral condyles. A pair of upright legs 48 are provided on plate 46 andthe legs 48 are provided with respective slots 49 to receive respectivepins 44 of bar 42. The slots 49 are part-circular in extent and have acommon center such that either pin 44 can ride its respective slot 49and change the angle of bar 42 relative to the caliper plate 46. Theends of the pins 44 are threaded and nuts 50 are engaged on the threadedends to lock the position of the pins 44 in the slots 49.

At the top of upper half 36 of the caliper means is an integralupstanding projection 60 which is integral with a guide bar 61. Theguide bar 61 extends substantially perpendicular to the plane of thecaliper halves 36, 37. The guide bar 61 has a bore 62 at one end thereofin which is slidably fitted an end of a rod 63 of an anterior caliperfeeler 64 for extension and retraction adjustment movement of theanterior caliper feeler 64. A nut 65 secures the position of the rod 63.At the end of the rod 63 of the anterior caliper feeler 64 is a sectorplate 66 which is pivotally supported at 67 by the rod 63. The sectorplate 66 has a part-circular surface 68 adapted to contact the anteriorsurface 13 of the femoral cortex. The surface 68 has its center at thepivotable support point 67.

In operation, the femur 1 is rotated 90° from the position shown in FIG.2 to the position in FIG. 3 or 5 so that the distal end of the femur 1is exposed. The bore 21 is formed in the femur 1 and the rod 20 isinserted into the bore 21. The tool 30 is then installed in the rod 20by fitting the bore 32 in sleeve 31 on the stub 24 of the rod 20projecting from the distal end of the femur 1. The posterior caliperfeelers 47 are respectively brought into contact with the posteriorsurfaces of the respective medial and lateral condyles. This effectivelyestablishes the position of plane T as described in FIG. 3.

A radially projecting tab 70 on the sleeve 31 is manually engaged torotate the sleeve 31 through angle A representing the angle determinedby the surgeon as explained previously. A scale 71 is provided toindicate the angle through which the sleeve 31, and thereby the rod 20,has been turned. The scale 71 comprises an index marker 72 on the sleeveand an angle scale 73 on the slider 34. The scale 73 is marked for leftand right femurs. For left femurs (described and illustrated in thedrawing) the sleeve and rod are rotated to the right (clockwise) whereaswhen the tool is mounted on a rod in the right femur, the sleeve and rodare rotated to the left (counter clockwise). When the scale 71 indicatesthe desired angle of rotation, the sleeve 31 is rotatably locked in theslider 34 by suitable means (not shown) and the rod 20 is driven intothe bore 21 of the femur 1 to be angularly secured thereon in thedesired rotational position relative to the plane T tangential to theposterior surfaces of the medial and lateral condyles. This is theposition shown in FIG. 9.

In order to set the caliper means in position to measure the distanceD′, the nuts 50 on pins 44 are loosened and the upper and lower caliperhalves 36 and 37 are rotated as a unit around pin 44 at the lateralfemoral condyle until the index marker 72 returns to its zero setting onthe scale 73 as shown in FIG. 10. The nuts 50 are then tightened and thecaliper halves are now in a position to measure distances perpendicularto the plane P tangent to the posterior surface of the lateral condyle.The capability of slidable movement of the slider 34 on the lowercaliper half 35 and of the caliper half 35 relative to bar 42 andposterior caliper feeler 45 permits the rotation of the caliper halvesabout pin 44 at the lateral condyle while the sleeve 31 and the slider34 are engaged with the stub 24 of rod 20.

The anterior feeler 64 is then positioned so that sector plate 66contacts the anterior surface 13 of the femoral cortex. A distance scale80 is provided between the upper and lower caliper halves 36, 35 andcomprises a marker 81 on leg 37 and a scale 82 on leg 38. The scale 82indicates the prosthesis size and hence is a measure of the distance D.The calibration is such that when the marker 81 is in correspondencewith a mark on scale 82 for a particular prosthesis, when thisprosthesis is utilized, the difference between D and D′ (the thicknesst₃ resected at the posterior condyle) will be substantially equal to thethickness of the prosthesis to be inserted. If the scale falls betweenprosthesis markings on scale 82, generally the smaller prosthesis isselected and the resected thickness of the lateral condyle will beslightly increased accordingly. The scale markings can also becalibrated with reference to the resected thickness t₁ at the medialcondyle to reflect the normally greater thickness resected thereat.

With the tool still mounted on the rod 20, FIG. 11, the anterior feeler64 is removed and a guide 90 is slidably fitted on guide bar 61. At thetop of the guide bar 61 another scale 91 is provided. The scale 91 ismarked in millimeters and represents the distance from a planeperpendicular to the rod and tangent to the high point of the distal endsurface of the more prominent of the medial or lateral condyles. Inother words, when the tool 30 remains on the rod 20 and is brought intoabutment with the condyles, this is the zero position of the scale 91.The guide 90 has four upstanding pegs 92 which fit into four holes 93 ofa distal end cutting guide 94.

The cutting guide 94 is provided with slots 95 extending in a planesubstantially perpendicular to the axis of stub 24. The slots 95 extendfrom the medial and lateral side surfaces of the cutting guide 94towards the center thereof. The slots 95 are adapted to guide a narrowcutting blade (not shown) for respectively cutting the medial andlateral condyles 6, 7 along planar cut 12. The slots 95 are separated bya solid, intermediate section 96.

The position of the slots 95 relative to the scale indicate thethickness t₂ to be resected by the planar cut 12 at the distal end ofthe femur 1. The invention contemplates that the thickness t₂ may beequal to the thickness t₃ determined by the measurement of distance D′.Therefore, the guide 90 is moved until the slots 95 are aligned with thedistance on scale 91 equal to the determined thickness t₃. The guide 90is then locked on guide bar 61 by suitable means (not shown).

Depending feet 97 are slidably mounted on cutting guide 94 in respectivepairs on opposite sides of each slot 95. After the cutting guide 94 hasbeen moved to its cutting position as indicated on scale 91, thedepending feet 97 are slidably moved to abut against respective portionsof the condyles. The feet 97 are provided with nail holes 98 and nails(not shown) are driven into the holes 98 to secure the cutting guide 94to the femur 1. A conventional cutting blade is then inserted in guideslots 95 to cut the distal ends of the condyles 6, 7 along the planarcut 12. The feet 97 nailed to the condyles prevent skewing or sliding ofthe cutting guide during the cutting operation.

The tool 30 is then removed from the rod 20 and a conventional APcutting guide 100 (FIG. 13) is fitted on the end of the rod 20 andabutted against the planar surface 12 now cut at the distal end of thefemur 1. The cutting guide 100 is provided with guide slots 101 and 102which can be precisely placed for guiding a cutting blade to produce theanterior and posterior cuts 10, 11 respectively. The cut 10 will beflush with anterior surface 13 of the femoral cortex and the cut 11 willbe at distance D therefrom. The AP cutting guide 100 also includesangular slots 103, 104 to form chamfer cuts 105, 106 on the femur 1which match corresponding angular surfaces 107, 108 on the kneeprosthesis 5.

FIGS. 14 and 15 illustrate a second embodiment of a tool 30A which is asimpler version of the first embodiment of FIGS. 5-10 and wherein thesame reference characters are used to designate like elements.

Essentially, the embodiment of the tool 30A of FIGS. 14 and 15 differsfrom that of FIGS. 5-10 in eliminating the rotatable sleeve 31 anddirectly engaging the stub 24 of rod 20 in bore 32 now provided directlyin the slider 34. The slider 34 thus serves as the engaging means forthe stub 24. The legs 48 on the caliper plate 46 are provided withspaced holes 149 instead of the continuous slot 49 of the embodiment ofFIGS. 5-10 and angular markings 173 are provided adjacent to the holes149 to indicate the magnitude of angle A between the caliper plate 46and bar 42, serving as a measurement plate, when the pin 44 is in therespective hole 149. In the illustrated embodiment in FIGS. 14 and 15,the holes 149 are placed to provide angulations of 0, 3, 5, 7 and 9°left and right between bar 42 and caliper plate 46.

In operation, the stub 24 is engaged in the bore 32 in slider 34 andpins 44 are placed in the 0° holes in respective legs 48. The caliperfeelers 47 are placed into tangential contact with the posteriorsurfaces of the medial and lateral condyles 6, 7 respectively. The pin44 in the leg 48 corresponding to the medial condyle is then removedfrom the 0° hole and placed in the hole 149 corresponding to the desiredangulation of the rod 20. This is shown in FIG. 15 where pin 44 is setin the hole 149 to angulate the bar 42, 7° relative to the caliper plate46 and thereby relative to the plane T tangent to the medial and lateralcondyles. By virtue of the slidable support of slider 34 in legs 37 andthe slidable support of cross leg 41 on bar 42, the tool 30A is capableof remaining in position on stub 24 and rotating around pin 44 at theposterior surface of the lateral condyle 7.

The measurement by the caliper means to determine the size of theprosthesis and the resected thickness t₃ at the lateral condyle iscarried out in the same way as in the first embodiment and the planarcuts are then made on the condyles as previously described.

As was described for the first embodiment of tool 30, it is alsopossible to effect measurement with the tool 30A to determine thicknesst₁ at the medial condyles and to utilize this thickness to establish thethickness t₂ distal cut 12.

Both the first and second embodiments have been described with regard tothe intramedullary rod 20 with radial flutes 23 to embed the rodsecurely in the bore 21 in the femur 1 to establish the datum orbenchmark position for attaching the cutting guide 94 to effect thedistal end cut 12 and thereafter the AP cutting guide 100 to effect theanterior and posterior planar cuts 10, 11. However, other suitable meanscan be employed to secure the angular position of the rod instead of theflutes 23. Moreover, since the rod 20 is ultimately removed from thefemur 1 after the planar cuts 10, 11, 12 have been made, the absence ofthe flutes 23 makes removal simpler.

FIGS. 16 and 17 illustrate a third modified embodiment of the tool 30Bwhich secures the angular datum position by use of a rod without flutes23. The same reference characters as in the first two embodimentsdesignate like elements.

In the third embodiment, the rod 20 is smooth and devoid of flutes 23.The rod 20 is rotated to its adjusted angular position, as in the firstand second embodiments, and in order to secure an angularly adjusteddatum position, lateral plates 110, 111 are secured to the legs 38 ofthe upper caliper half 36. Each plate 110, 111 contains two verticalrows 112 of overlapped holes 113. The rows 112 are designated for rightand left femurs and the holes 113 are respectively graduated in sizeorder from the scale 82. When the caliper means of the tool 30B has beenrotated to the desired degree of angulation, pins 115 or similarfasteners are placed in the appropriate holes 113 in the lateral plates110, 111 and secured in the distal ends of the medial and lateralcondyles so that the pins 115 project from the distal ends of thecondyles. The pins 115 establish an angular datum position representingthe rotation of the tool. The steps of measurement of prosthesis size,and of effecting the planar cut with the guide 94 are carried out as inthe previously described embodiments. However, after the distal end cut12 is made, the tool 30B is removed leaving the pins 115 in place in thecondyles, the rod 20 is removed from the femur 1, and a guide 100′, FIG.20, is mounted on the pins 115 which serve to accurately position theguide 100′ so that the slots 101-104 will be precisely located for exactplacement of the cuts 10, 11, 105 and 106. The guide 100′ has holes 116to receive the pins 115 which are precisely located with regard to theslots 101-104 to insure accurate location of the cuts when the guide100′ is mounted on the pins 115. After the cuts have been made, the pins115 are removed from the condyles. As evident from the above, theembodiment contemplates the use of the pins 115 as the means to providethe datum position for the cutting guide 100′ in lieu of the rod 20. Theuse of the plates 110, 111 and of the pins 115 is applicable to theother embodiments as well.

FIGS. 18 and 19 illustrate a fourth modified embodiment of the tool 30Cwhich is a simplified version of the second embodiment of FIG. 14 anduses the same reference-characters to designate like elements.

The tool 30C utilizes slider 34 which engages the rod end 24 and isslidably engaged in the legs 37 of the lower caliper half 35. The legs37 of the lower caliper half 35 are slidably engaged with the legs 38 ofthe upper caliper half 36.

At its lower end, the lower caliper half 35 includes a cross bar 141from which a leg 142 depends. The leg 142 supports a pivot 143 whichslidably rides in a slot 144 in a bracket 145 integral with posteriorcaliper plate 146. The posterior caliper plate 146 is similar to caliperplate 46 of the second embodiment and includes posterior caliper feelersfor contacting the medial and lateral condyles 6 and 7. The slot 144extends substantially parallel to the caliper plate 146 in the plane oftangential contact of the posterior feelers with the posterior surfacesof the medial and lateral condyles. An angle scale 147 is providedbetween the leg 142 and the bracket 145.

In the initial position of the tool, the slider 34 is fitted on the end24 of the rod and the posterior feelers are brought into tangentialcontact with the medial and lateral condyles. The caliper means 35, 36are rotated, while the rod 24 is held fixed, until the angle scale 147reads zero. The pivot 143 is disposed in the slot 144 substantially inthe plane T tangent to the posterior surfaces of the medial and lateralcondyles. The tool 30C is then rotated to cause the end 24 to rotatethrough an angle A. corresponding to the determined angle of rotation.The angle A is read on the angle scale 147. The pin 143 undergoesslidable movement in slot 144 while the slider 34 undergoes slidablemovement in lower caliper half 35 to accommodate the rotation of thetool. The pin 144 remains in the tangential plane T. The scale 80 is ameasure of the distance from the anterior feeler in contact with theanterior femoral cortex and the pin 143 along a perpendicular line fromthe anterior femoral cortex to a plane P passing through the pin 144 andinclined relative to posterior caliper plate 146 by the angle ofrotation A of the tool. Any difference between the distance from pivotpoint 67 to the surface 68 of the sector plate 66 and the correspondingdistance measured along the perpendicular to the incline plane P isnegligible and even for an angle A of 12° the difference will be lessthan one-third mm.

As an alternative to the slot 144, the bracket 145 can be provided witha series of holes representing different angles of the caliper means 35,36 relative to the plate 146, corresponding to different angles A, as inFIG. 14. The holes are provided along the axis of slot 144 in order tobe in tangential plane T of the posterior feelers on the posteriorsurfaces of the condyles. When the pin 143 is secured in a respectivehole the caliper means is secured at the angle designated by theassociated hole. In the use of this alternative, with the tool not yetfitted on the end 24, the angle of the caliper means is set by insertingthe pin 143 into the selected hole and the posterior feelers on plate146 are brought into tangential contact with the condyles 6, 7. The toolis then fitted on the end 24 which now assumes the angle of the calipermeans relative to the plate 146. The rod 20 is then driven into thefemur 1 as before, or alternatively, as in the embodiment of FIGS. 16and 17, pins 115 are installed in the condyles through holes in plates110, 111 installed on the upper caliper half of the tool. The subsequentoperations are the same as previously described.

FIGS. 21-33 illustrate a fifth modified embodiment of a tool 30D whichis a simplified version of the first four embodiments of FIGS. 1-20 andwherein like reference characters are used to designate like elements.Preferably, the tool 30D is used in connection with a GENESIS II TotalKnee System supplied by Smith & Nephew Richards, Inc. of Memphis, Tenn.It should be realized, however, that the tool 30D can be adapted to beused with knee systems of other manufacturers.

Referring now to FIG. 33, there is shown a GENESIS II femoral prosthesis198. The thickness of the distal femoral condyles of the prosthesis isabout 9.5 mm (about 9-9.5 mm), i.e., the thickness of the distal medialfemoral condyle 204 and the distal lateral femoral condyle 206 are aboutthe same.

The prosthesis 198 has a 30 external rotation or varus angulation builttherein. This is accomplished by altering the thickness of the femoralcondyles posteriorly. For example, the thickness of the posteriorlateral femoral condyle 200 of the prosthesis is about 3 mm thicker(about 2.5-3 mm) than the posterior medial femoral condyle 202, assumingthat the most prominent portions of the medial and lateral condyles aretwo inches apart. The difference of thickness of the posterior condylesof the prosthesis will vary directly with the distance between thecondyles. The GENESIS II tibial prosthesis assembly, not shown, has atibial baseplate (metal) thickness of about 2 mm and a minimal tibialprosthetic (plastic) thickness of about 7.5 mm.

When using the tool 30D and the GENESIS II prosthesis 198, the jointline will be realigned parallel to the floor. This changes a normally 3°varus angle to 0°. A 3° angle amounts to approximately 1.5 mm per linearinch. Assuming the tibio femoral weight-bearing area is 2 inches aparton average, then 3 mm more laterally than medially must be resected fromthe tibia to achieve the resection parallel to the floor. To achieve arectangular extension space and a trapeziodal flexion space, it followsthat 3 mm more from the distal medial femoral condyle than the distallateral femoral condyle must also be resected. The posterior condyles,however, are neutrally resected.

Referring now to FIGS. 21-33, once the bore 21 is formed longitudinallyin the shaft 9 and in the condylar region 4 of the femur 1, the tool 30Dis fitted over the rod 20 until it contacts the distal femur, i.e., thedistal end of the femur 1. Before the tool 30D is fitted over the rod20, the tool 30D is first fitted with a collet 206 which is similar tothe stub 24. Like stub 24, collets having different angles varying about5-7° may be provided and selection is made based on the anatomicalcondition and other conditions of the patient. The collet 206 is similarto the valgus angle bushing available from Smith & Nephew Richards, Inc.

The tool 30D is somewhat similar in structure to, but an improvedversion of, the valgus alignment guide and/or valgus alignment assemblyavailable from Smith & Nephew Richards, Inc. The tool 30D includes adistal femoral sizer made up of a lower half 208 and an upper half 210slidable in the lower half 208. When the distal femoral sizer is fittedwith collet 206, collet 206 fixes the angle of the distal femoral sizerand may be referred to as a valgus alignment guide.

The lower half 208 includes a pair of posterior caliper feelers 47 forrespectively contacting the posterior surfaces of the medial and lateralcondyles. The caliper feelers 47 can be elongated to accommodate smallerand larger femurs, corresponding to prosthesis sizes 1-5 and 4-8respectively.

The tool 30D includes a graduated scale 212. The graduated scale 212includes markings 213 on the upper half 210 and a marker 214 on thelower half. The markings 213 on the graduated scale 212 indicateprosthetic sizes and hence is a measure of the distance D or S. Forexample, the markings 213 in FIG. 21 indicate prosthetic sizes 3-8. Theupper half 210 can be adapted to indicate other prosthetic sizes aswell.

The lower half 208 includes scale 215 to indicate differences in sizebetween respective prosthetic sizes, i.e., the number of millimetersover or under the prosthetic size. In a preferred embodiment, the scale215 is calibrated in one millimeter increments. The calibration is suchthat when the marker 214 directly corresponds with a mark 213 on thescale 212 for a particular prosthesis, e.g., size 4, when this size 4prosthesis is utilized, the difference between D and D′ (the thicknesst₃ resected at the posterior condyles and the distal femoral condyles)will be substantially equal to the thickness S (FIGS. 4 and 34) of thesize 4 prosthesis to be inserted.

If the marker 214 falls between prosthesis markings 213 on scale 215,generally the smaller prosthesis size is selected and the resectedthicknesses of the posterior condyles and the distal femur will beslightly increased accordingly. For example if the marker 214 falls oneincrement, i.e. one millimeter, beyond prosthesis size 4, then theresected thickness at the posterior condyles will be the averagethickness of the posterior condyles of the size 4 prothesis (e.g., 19.5mm) plus 1 mm. similarly, the resected thickness of the distal femoralcondyles may be electively increased 1 mm, i.e., 9.5 mm plus 1 mm.

It should be realized that if a surgeon were to choose the largerprosthesis, then the marker 214 and the scale 215 would indicate howmuch less thickness from the prosthetic size would be resected at theposterior and distal femoral condyles. In this case, appropriatecompensation must be made on the distal femoral resection and possiblythe proximal tibial resection, depending on the deformity of the knee,to achieve satisfactory motion and ligament balance.

The tool 30D includes an anterior-posterior (A-P) measuring guide oranterior caliper feeler 64 which along with the posterior caliperfeelers 47 measure distance D′. The A-P measuring guide 64 includes atab 216 which allows the A-P measuring guide to be releasably attachedto the tool 30D.

The A-P measuring guide 64 is somewhat similar in structure to, but animproved version of, a femoral sizing guide available from Smith &Nephew Richards, Inc. The A-P measuring guide 64 includes a rod 63 and asector plate 66 adapted to contact the anterior surface 13 of thefemoral cortex. Unlike the tool 30 of the first preferred embodiment ofFIGS. 1-3, the sector plate 66 need not be pivotally attached to the rod63.

The tool 30D is also adapted to be used in connection with a distalfemoral resection caliper 88, a distal femoral cutting block 89 (FIGS.24-28) and an A-P cutting block 100 (FIGS. 29-31). The distal femoralcutting block 89 is used to resect the distal ends of the femur 1. TheA-P cutting block 100 is used to resect the posterior medial and lateralcondyles, to make the final anterior resection and to make the posteriorand anterior chamfer resections as described above. The distal femoralcutting block 89 and the A-P cutting block 100 are somewhat similar instructure to, but an improved version of, the distal femoral resectionstylus and cutting block, and the femoral A-P cutting block,respectively, available from Smith & Nephew Richards, Inc. Like the A-Pmeasuring guide 64, the distal femoral cutting block 89 (and resectioncaliper 88 when joined, as explained below) are releasably attached totool 30D by tab 218.

Referring now to FIGS. 21-33, in use, once the tool 30D with theproperly angled collet 206 is fitted over the rod 20, which is insertedin the bone 21 of the femur 1, the tool 30D is made to contact thedistal femur 1. As best seen in FIGS. 23 and 26, the side of tool 30Dthat contacts the distal femur 1 should include a 3 mm lateral offset220 to contact the distal surface of the lateral femoral condyle. Thisensures that the distal resection is substantially parallel to theproximal tibial resection in the medial lateral plane, and that theresultant distance between the tibial and femoral resections will besubstantially equal to the thickness of the combined tibial and femoralprosthesis in flexion and extension.

In an alternative embodiment, if collet 206 is angled 8-10° instead of5-7°, the 3 mm lateral offset 220 is not necessary. The 8-10° angulationis preferable because it reflects the true angulation of the distalfemur.

Next, external rotation must be oriented from the posterior condyles (orany other consistent anatomic landmark). This requires adjustableposterior feelers or “feet” 47 to contact the posterior condyles at 3°of external rotation, or to be able to compensate for deformities andachieve posterior proper rotation.

To achieve the 3° external rotation, the tool 30D is then rotated sothat the posterior caliper feelers 47 contact both correspondingposterior surfaces of the medial and lateral condyles (FIGS. 22 and 23)assuming equal or no bone substance loss. This sets the rotation orangle of the preliminary anterior resection 10 and the posteriorresection 11 which is made by the A-P cutting block 100 (FIGS. 29-31),and equal amounts of substance will be resected from the medial andlateral posterior condyles. The rotation or angle of the posteriorresection 11 is also set because an anterior portion 248 of the A-Pcutting block 100 rests on the preliminary anterior resection 10 andthus orients the posterior resection 11 from the rotation or angle asthe anterior resection 10. Referring now to FIG. 23, nails 222 shouldthen be inserted in nail holes 224 to secure the lower half 208 to thedistal femur.

If the posterior surfaces have unequal bone loss, the correspondingcaliper feeler 47 should be made to contact the posterior surface withthe least amount of bone loss. The tool 30D should then be rotated onthe rod 20 so that the other caliper feeler 47 corresponding to theposterior condyle with the greater amount of bone loss is a distanceaway from that posterior condyle about equal to the amount of bone loss.This sets the rotation, or angle, of the preliminary anterior resection10 and the posterior resection 11 which is made by the A-P cutting block100 (FIGS. 29-31). Unequal amounts of substance may now be resected fromthe medial and lateral posterior condyles.

Referring now to FIGS. 34-38, in an alternative embodiment, clips 300sized to make up for bone loss to the posterior condyles can be added tothe posterior feelers 47. With clips 300, tool 30D does not need to berotated as explained above to achieve the 3° external rotation.Preferably, clips 300 are made in 2, 4, 6, 10, and 12 mm sizes, althoughclip 300 can be made of any other appropriate size. The user of the tool30D can estimate the amount of bone loss to the nearest clip size. InFIGS. 34-38, clip 300 is attached to the posterior feeler 47corresponding to the medial posterior condyle because the medialposterior condyle suffered bone loss.

If both the medial and lateral condyles suffer bone loss, then the userof tool 30D uses the appropriately sized clip 300 based upon relativebone loss between the medial and lateral condyles. For example, if themedial posterior condyle suffers 6 mm bone loss and the lateralposterior-condyle suffers 2 mm bone loss, then a 4 mm clip 300 will beattached to posterior feeler 47 corresponding to the medial posteriorcondyle.

The clips 300 can be attached to the posterior feelers 47 by any of theknown methods. Preferably, posterior feelers 47 include a slot 302 andedges 304 which receive a tab 306 and grooves 308, respectively, formedin clip 300. Clips 300 may even include a spring activated post 310 orthe like to secure clip 300 to posterior feelers 47 once slot 302 andedges 304 of the posterior feelers 47 receive tab 306 and grooves 308 ofclip 300. Posterior feelers 47 may also include posts 310 to even moresecurely attach clips 300 to posterior feeler 47.

In the first preferred embodiment of the invention, the scale 71 shouldbe set to rotate the sleeve 31 and thereby the rod 20 through angle A at1° for every millimeter of bone loss. For example if the surgeondetermines that there is 2 mm bone loss at one of the posteriorcondyles, the index marker should be set to correspond to a 2° angle onthe angle scale 73. The sleeve 31 is then rotatably locked in the slider34 and the rod 20 is driven in the bone 21 of the femur 1 to beangularly secured thereon in the desired rotational position relative tothe plane T targeted to the portion surface of the medial and lateralcondyles. See FIG. 9.

In order to set the caliper means in position to measure the distanceD′, the nuts 50 on pins 44 are loosened and the upper and lower caliperhalves 36 and 37 are rotated as a unit around pin 44 at the lateralfemoral condyle until the index marker 72 returns to its zero setting onthe scale 73 as shown in FIG. 10. The nuts 50 are then tightened and thecaliper halves are now in a position to measure distances perpendicularto the plane P tangent to the posterior surface of the lateral condyle.

In the fourth preferred embodiment of the invention, the tool 30C isrotated to cause the end 24 to rotate through angle A corresponding tothe 2° angle of rotation. The angle A is read in the angle scale 147.

It should be realized that as explained above, if a prosthesis otherthan a GENESIS II prosthesis is used, i.e., a symmetrical prosthesis,the posterior condyles will be resected asymmetrically to reflect the 3°external rotation that was otherwise built into the GENESIS IIprosthesis. This angulation may be greater than or less than 3° tocompensate for any bone loss posteriorly.

Referring back now to tool 30D, in order to set the caliper means inposition to measure the distance D′, the upper half 210 of the tool 30Dfitted with the anterior caliper feeler 64 is then lowered until thesector plate 66 of the anterior caliper feeler 64 contacts the lateralportion of the anterior cortex, i.e., the sector plate 66 should contactthe lateral side of the anterior cortex (FIGS. 22 and 23). The marker214 then indicates a prostheses size S or distance D. If the marker 214falls between two prosthetic sizes, normally the smaller prosthetic sizeis chosen. The upper half 210 is then fixed to the distal femur byinserting a nail 226 in the nail hole 228 that corresponds to thesmaller chosen prosthetic size.

A measurement is now made to determine the appropriate size A-P cuttingblock 100 to later be used to resect the posterior medial and lateralcondyles. The approximate size cutting block 100 corresponds to thechosen prosthetic size. If the marker 214 fell between two prostheticsizes and the smaller size is chosen, i.e., anterior referencing, ameasurement must be made to determine how many millimeters extra wouldbe resected posteriorly (i.e., the thickness of the prosthesisposteriorly plus the number of mm over resection). This measurement isthen taken from the scale 215 and is equal to the number of millimetersthe marker 214 is away from the smaller prosthetic size. Thismeasurement is then added to the average thickness of the posteriorcondyles of the prosthesis to determine the posterior resections. Eachtype of prosthesis has its own average thickness. For example, if themarker 214 indicates 1 mm greater than prosthetic 198 size 3, 1 mm extrawill be resected posteriorly. The total posterior resection would thenbe the average thickness of the posterior condyles of the prosthesis 198(e.g., 8.5 mm) plus 1 mm for a total thickness of 9.5 mm.

With the tool 30D still mounted on the rod 20, the anterior caliperfeeler 64 is removed from the upper half 210 by depressing the tab 216.A saw blade, not shown, is then inserted into guides or slot 230 to makea preliminary cut. of the anterior condyles to meet the surface of theanterior cortex in proper rotational alignment in the mediolateralplane.

The distal femoral cutting block 89 secured to distal femoral resectioncaliper 88 is then attached to the upper half 210 of tool 30D. Distalfemoral resection caliper 88 is releasably attached to distal femoralcutting block 89 through a channel 234 fixed therein. Distal femoralresection caliper 88 is secured to distal femoral cutting block 89 by acam mechanism 236 and to the upper half 210 by tab 218.

The distal femoral resection caliper 88 includes a sliding scale 238that is calibrated at one millimeter increments from the average size orthickness of the distal femoral condyles of the prosthesis. The averagesize or thickness of the distal femoral condyles of a prosthesis rangesfrom about 6 mm to 12 mm depending on the particular prosthesis chosen.A typical thickness of the distal femoral condyles of prosthesis 198 isabout 9.5 mm.

The distal femoral cutting block 89 should be inserted on the upper half210 until it abuts the resected surface of the anterior cortex (FIGS.25,26). The cutting block 89 should then be set at “size” plus (orminus) the previously taken measurement of how many extra (or fewer)millimeters would be resected posteriorly, i.e., 1 mm, at the surgeon'sdiscretion. As explained above, “size” equals the average of theexpected resection of the medial and lateral distal femoral condyles.This equals 9.5 mm assuming normal anatomy. This will resect 11 mm fromthe distal medial femoral condyle and 8 mm from the distal lateralfemoral condyle assuming a two inch distance between the two, i.e., thetwo most prominent portions of the distal femoral condyles.

The distal femoral cutting block 89 is then locked into place on slidingscale 238 by the cam mechanism 236. The distal femoral cutting block 89is then secured to the anterior cortex by nails 240 through nail holes242.

The rod 20 is then removed from the tool 30D. The cam mechanism 236 isdisengaged and the distal femoral resection-caliper 88 and the tool 30Dshould be removed from the distal femoral cutting block 89. Only thedistal femoral cutting block 89 should remain on the femur 1 (FIG. 28).

The distal femur should then be resected along the mediolateral plane244 of the distal end 246 of the distal femoral cutting block 89. Thepreliminary anterior and final distal cuts 10 and 12, respectively, havenow been made as illustrated in FIGS. 1 and 4a.

The plane 244 or cut 12 should be substantially parallel in themediolateral plane to the proximal tibial resection, i.e., parallel tothe floor, assuming normal ligament balance. If the ligaments are notnormally balanced, then the ligaments should be released by any of theknown methods until the planes are parallel in the mediolateraldirection.

Referring now to FIGS. 38-41 in an alternative embodiment, if collet 206is angled 8-10° and the 3 mm lateral offset 220 is not used as explainedabove, distal femoral resection caliper 88 must compensate for the 3°increase in the angle of collet 206. Preferably, distal femoralresection caliper 88 compensates for the increase in the angle of collet206 by itself being angled 3° as shown in FIGS. 38, 40, 41. For the leftfemur as shown in FIG. 38, distal femoral resection caliper 88 is angled3° laterally as shown in FIG. 40 (i.e., follows the direction of theintramedullary rod). For the right femur, not shown, distal femurresection caliper 88 is angled 3° laterally as shown in FIG. 41 (andwould also follow the direction of the intramedullary rod). Theangulation of the distal femoral resection caliper 88 insures that theangle of the distal femoral resection corresponds to the medio-lateralplane of the tibial resection in a normal knee. Thus if one of thedistal condyles suffers bone loss, the distal resection will remain atthe proper level. In FIG. 38, there is shown a collet 206 angled 9°.Using distal femoral resection caliper 88 angled at 3° insures that thedistal femoral resection is made 3° less, or 6°.

Referring now to FIGS. 29-32, the distal femoral cutting block 89 shouldbe removed from the distal femur, and the appropriately sized A-Pcutting block 100 should be inserted thereon. The A-P cutting block 100is used to make the final anterior resection 10 and to resect theposterior surfaces of the medial and lateral condyles 11. If the flexionspace is of concern, the preliminary anterior resection, distal femoralresection, and posterior condylar resection should be performed.Preferably, the flexion and extension spacing or “balance” with theappropriately-sized spacers are tested before continuing. See FIGS.48-49.

The A-P cutting block 100 is placed onto the distal femur secured byangled nails through the sides of the cutting block 100, not shown. TheA-P cutting block 100 includes an anterior portion 248 that sits flushwith the anterior cortex of the femur 1. If desired, the A-P cuttingblock 100 can also be secured to the distal femur by nails (not shown)in nail holes 250. The A-P cutting block 100 should now sit flush withthe cut anterior surface 10 and the distal surface 12.

The A-P cutting block 100 includes slots 102 and 101 which are preciselyplaced for guiding a resector or cutting blade to produce the finalposterior and anterior cuts 11, 10 respectively. Because of theasymmetric buildup of metal on the posterior condyles of the GENESIS IIfemoral prosthesis 198, e.g., about 2.5-3 mm thicker on the posteriorlateral condyle, the posterior femoral resection 11 must be altered toaccommodate this difference. The resultant posterior femoral condylarjoint line should be parallel to the resultant tibial joint line, i.e.,parallel to the floor.

The posterior femoral resection 11 should be approximately 3° of varus(e.g., if using the Genisis II knee) in the mediolateral planereferenced from the horizontal assuming no wear or equal wearposteriorly. The A-P cutting block 100 assures this due to its alignmentwith the preliminary anterior femoral condyle resection 10. The A-Pcutting block 100 is so aligned because the anterior portion 248 restson the preliminary anterior cut 10 which has already been resected atthe desired rotation or angle. The posterior condylar resection will beequal posterior medially and posterior laterally assuming no wear orequal wear of the posterior condyles. Moreover, the posterior cut 11will be made in a constant relationship, e.g., diverge 3°, from theproximal tibial resection. In other words there will be an opening wedgelaterally.

As explained above, if there is unequal wear, then tool 30D would havebeen rotated appropriately to account for the asymmetric loss ofsubstance. The posterior resections will not be equal posterior mediallyand laterally under this circumstance.

The A-P cutting block 100 also includes angular slots 103 and 104 toform chamfer cuts 105, 106 which also match corresponding angularsurfaces 107, 108 on the prosthesis 198. Preferably, the femur 1 shouldbe resected in the following order: the posterior resection 11, theposterior chamfer 106, the final anterior resection 10 and the anteriorchamfer 105 (see FIG. 4a). The A-P cutting block 100 is then removed andthe prothesis 198 is installed on the distal femur by any of the knownmethods.

As shown above, since the prosthetic femoral condylar dimensions were9.5 mm distally and posteriorly, a “standard” resection would be set toresect 11 mm from the distal medial and posteromedial condyles, and 8 mmfrom the distal lateral and posterolateral condyles. This would thenproduce a 9.5 mm resection at the midline. When combined with the tibialresection, explained below, this would give a 19 mm rectangular space toreceive the prosthetic components.

Preferably, the instrument system of the present invention is forfemoral resection and replacement, tibial resection and replacement andpatellar resection and replacement, i.e., a total knee replacementsystem. Preferably, in the total knee replacement system of the presentinvention, the tibia is resected before the femur and the tibia thenreresected, if necessary, to properly articulate the tibial and femoralprosthesis. It should be realized, however, by those skilled in the artthat the tibia and femur can be resected and replaced in any order.

Referring now to FIGS. 42-44, there is shown a tibial resection guide400 of the present invention mounted on tibia 2. Tibial resection guide400 is similar to, but an improved version of, the tibial alignmentassembly marketed by Smith & Nephew Richards, Inc., in Memphis, Tenn.under the PROFIX® total knee system and adapted to GENESIS II prostheticdimensions and specifications.

Tibial resection guide 400 includes a bore 402 for receiving a reamerrod 404 therethrough. Bore 402 is drilled in tibial resection guide 400at a 3° posterior tilt, i.e. tilted down from the anterior to posterior,or down from the horizontal, 3°. Tibial resection guide 400 is mountedon tibia 2 by any of the known methods.

Initially, the knee should be exposed in the standard fashion evertingthe patella. The anterior cruciate ligament and the PCL should bereleased, and the medial osteophytes removed, if necessary. Preferably,using a standard femoral drill, e.g., ⅜″, the proximal tibial medullarycanal 406 is opened at, or just posterior to, the tibial attachment ofthe anterior cruciate ligament. The reamer rod 404 is then placed in thedrilled tibial shaft just anterior to and between the tibial spines byany of the known methods.

Tibial resection guide 400 is mounted on rod 404 in the manner shown inFIGS. 42-44. Tibial resection guide 400 includes a pair of styluses 408rotatable in tibial resection guide 400. Preferably, the styluses arespaced about 2 inches apart. Styluses 408 are independently rotatable sothey can contact the highest, or the most intact side, of the tibialplateau. Styluses 408 include angled or curved foot extensions 410.Preferably foot extensions 410 are angled so they extend approximately3-4 mm further posterially than reamer rod 404.

Once a stylus 408 is made to contact the most intact or highest point onthe tibial plateau, that particular stylus 408 remains stationary whiletibial resection guide 400 is moved up or down rod 404 until itcoincides with an “M” marking 412 if the most intact side is the medialside, or with “L” marking 414 if the most intact side is the lateralside. It is not necessary to use both styluses. Tibial resection guide400 is then secured in that position by for example tightening a slidingscrew. The markings 412, 414 set the proper tibial resection.Preferably, for a tibial prosthesis 9.5 mm thick, the proper resectioncorresponding to the “L” marking 414 is 11 mm and 8 mm for the “M”marking 412, thus representing a 3 mm difference between the markings,assuming the styluses are two inches apart. One millimeter or moremarkings can be utilized therebetween. For prostheses with differingthicknesses, the resection lengths for the markings 412, 414 areadjusted taking into account that the tibial plateau variesapproximately 1.5 mm per inch. Thus, the thickness of the prosthesis,e.g., 9.5 mm, should represent an average thickness between the mediallateral resection, namely 8 mm and 11 mm, respectively.

Tibial resection guide 400 is now in the proper position to remove thedesired amount of bone described above, i.e., resect at 8 mm medially or11 mm laterally. At this time it is preferable to protect the posteriorcruciate ligament (PCL) if still intact.

To resect the bone, a resector is inserted through slot 416 by any ofthe known methods. Because of the 3° proximal medio-lateral varus tiltof the tibia, the bone is resected on a 3° valgus medio-lateral tiltrelative to the tibial plateau. Regardless of the tilt, using either anintramedullary or extramedullary rod, the resultant resection of thetibial plateau in the medio-lateral plane must be parallel to the floor.

Referring now to FIG. 43, because bore 402 is drilled in tibialresection guide 400 at a 3° posterior tilt, i.e. tilted down from theanterior side to the posterior side 3°, tibia 2 is resected 3° down fromthe horizontal, i.e., tilted higher anteriorly than posteriorly.

Preferably, slot 416 of tibial resection guide 400 extends through mostof its width, and does not include a stop in the center like tibialresection apparatus of the prior art. Without such a center stop, betteraccess is afforded to the tibia.

In a preferred embodiment, tibial resection guide 400 includes stops 418at the ends thereof. Stops 418 protect the patellar tendon and themedial and lateral ligaments.

Referring now to FIG. 45 there is shown an alternative embodiment to thepresent invention. FIG. 45 shows a tibial external alignment guide 420.Preferably, rod 404 should be angled 3° to account for the 3° posteriortilt bored into tibial resection guide 400 as explained above. Tibialexternal alignment guide 420 is otherwise constructed, and resects tibia2, in the same way as tibial resection guide 400.

Now that tibia 2 and preferably femur 1 have been resected, tibialsecondary finishing apparatus is employed to achieve a properlyarticulated knee in flexion and extension. For example, tibial resectionguide 422, FIG. 50 described below, can be used to downsize, i.e.,reresect, tibia 2, versus downsizing femur 1, i.e., resect more bone offof, to gain increased flexion if the knee is tight following the femoraland tibial resections.

Referring now to FIGS. 46-47, there is shown a spacer apparatus which isused to check the space between the tibial and femoral surfaces inflexion and extension after the appropriate femoral and tibialresections. The spacer apparatus is typically necessary only in caseswhere the spacing is put in question, e.g., where the knee has a complexdeformity or a severe loss of motion. The goal is to cut off the leastamount of bone and have proper ligament balance medially and laterallyin flexion and extension. The ligament balance should be solid inextension and slightly loose in flexion. The spacer apparatus isadvantageous because it determines how much additional bone to resectbefore the bone is actually resected.

Referring now to FIG. 46, spacer apparatus includes paddle 424 having anextension spacer 426 and a flexion spacer 428 located at opposite endsthereof. As shown in FIG. 46A, flexion spacer 428 tapers from 10.5 to 7mm in thickness. As shown in FIG. 46B, extension spacer 426 is uniformly7 mm thick.

Paddle 424 can be used in connection with snap-on spacers, not shown,which are available from any of the know suppliers and can be secured topaddle 424 by any of the known methods. The snap-on spacers are used toincrease the thickness of extension and flexion spacers 426, 428.Preferably, the snap-on spacers should come in sizes of 2-16 mm or 2-27mm, and be available in 2 mm increments, e.g., 2, 4, 6 mm etc.

Heretofore, paddles of the prior art had extension spacers 19 mm thickand flexion spacers that tapered from 19-20 mm in thickness. Thesepaddles are disadvantageous because (1) they can not be used in spacesless than 19 mm thick; and (2) they do not accommodate ligamentouslaxity (trapezoidal space).

Paddle 424 and snap-on spacers are used in accordance with known methodsto ensure a properly articulated knee in flexion and extension andproper ligament balance.

Referring now to FIG. 50, there is shown a tibial reresection guide 430that is used to take additional bone off of tibia 2 if, for example,this is found to be necessary as a result of using the spacer apparatusdescribed above. Tibial reresection guide 430 is similar to, but animproved version of, the tibial secondary prep guide marketed by Smith &Nephew Richards, Inc., in Memphis, Tenn. under the PROFIX® total kneesystem.

Like tibial resection guide 400, tibial reresection guide 430 includes abore 432 drilled in the reresection guide at a 3° posterior tilt, i.e.tilted down from the anterior to posterior, or down from the horizontal,3°. Tibia 2 is reresected an appropriate amount using any of the knownmethods.

Referring now to FIGS. 53-57, there is shown an apparatus in accordancewith the present invention for patellar replacement. The apparatus ofthe present invention allows for medialization of the patellarprosthesis and offers the following advantages:

containment with circumferential bone

load sharing with the “intact” patella

maintenance of the patellar ridge

“replaced” surface conforming to trochlear notch

minimal sacrifice of the patellar bone.

Referring now to FIG. 53, a patellar clamp 500 is shown therein. Theknee must first be fully extended and the patella completely exposed onthe tendinous surface. The patella is then inverted and the patellarclamp 500 placed on the lateral aspect of the patella. Patellar clamp500 is similar to, but an improved version of, the patellar clampmarketed by Smith & Nephew Richards, Inc., in Memphis, Tenn. under thePROFIX® total knee system.

Patellar clamp 500 is first used to measure the thickness of patella 502so the surgeon knows how much of patella 502 will be left whileaccommodating the patellar insert 504, FIG. 57. It is undesirable toleave too little bone. It is desirable to have patellar insert 504 wellcontained and stable in the patellar bone supporting itcircumferentially.

To measure the thickness of patella 502, the patella is placed betweenan appropriately sized collet 506 and a base plate 511. Collet 506 hasfour prongs 508 equally spaced around and over the peak 509 of thepatella 502. Prongs 508 are separated by arcuate sections 512. Collet506 is then centered over the patellar ridge and patellar clamp 500 istightened by a thumb screw 513 or by any of the known methods.

Preferably, collet 506 is pivotably hinged to the arm 507 of patellarclamp 500, FIGS. 53, 53 a. This hinged arrangement allows all of theprongs 508 to contact the patellar peak 509 if it is disposed at anangle.

The thickness of patella 502 for purposes of the present invention is adistance d between where prongs 508 intersect the patella, and baseplate 511. As a result, patella 502 is reamed or drilled from whereprongs 508 intersect patella 502.

Patellar clamp 500 includes a scale 514, FIG. 54, located at an endthereof which measures distance d. The scale determines if patella 502is thick enough for reaming. In FIG. 54, for example, distance d isdetermined to be 20 mm.

Next, patellar reamer 516 corresponding in size to collet 506, is placedin patellar collet 506 to drill or ream away the required amount ofpatella 502 from where prongs 508 intersect patella 502 to accommodatepatellar insert 504 by any of the known methods. In a preferredembodiment, patellar reamer 516 includes a depth scale 518, FIG. 55,located therein to indicate how much patellar reamer 516 reams or drillsinto patella 502. Preferably, markings 518 correspond to the thicknessof patellar insert 504, e.g., 8 mm or 12 mm.

By way of example, in FIGS. 55-56, (hinged embodiment not shown) scale514 measured a patellar thickness of 20 mm. As a result, if a surgeondecides to use an 8 mm patellar insert 504, and accordingly ream patella502 8 mm's, he then knows there will be 12 mm of bone left anteriorly,which is a sufficient amount left for reaming and to accommodatepatellar insert 504. As there is a significant amount of intratendonouspatella distally, at least a 4-5 mm margin superiorly (if possible)should be left.

The surgeon would then ream patella 502 8 mm from where prongs 508intersect patella 502 or until depth scale 518 indicates 8 mm.Preferably, it is recommended to rongeur the excess substance superiorlyand inferiorly to level off the patellar ridge. The surgeon would theninsert patellar insert 504 by any of the known methods, FIG. 57.

Referring now to FIGS. 58-59, there is shown an improved nail and slaphammer apparatus of the present invention. FIG. 58 shows an improvednail 600 of the type to secure apparatus, e.g., distal femoral cuttingblock 89, FIG. 59, to femur 1, or tibia 2.

Nail 600 includes two flat sides 602 adjacent two round sides 604. Thisallows nail 600 to be drilled rather than hammered into the bone.Preferably, nail 600 is lengthened ½-¾″ from prior art nails, andincludes a stop 606 to prevent nail 600 from being drilled too far intothe apparatus. This leaves sufficient room between the head 608 of thenail and slap hammer 609 to remove nail 600 as shown in FIG. 59. Nail600 further includes a hexagonal head 608 so the nail can be used inconnection with a quick-release chuck.

Referring now to FIG. 59, slap hammer 609 includes a flat shaft 610which creates a path of travel for a head 611 to travel up and down.Preferably, shaft 610 should be flat, and a channel in head 611, notshown, similarly shaped, to prevent head 611 from spinning on shaft 610.Preferably, slap hammer 609 should include a claw like end 612 to moreeasily secure nail 600 and remove it from the bone.

As mentioned above, an objective of the apparatus of the presentinvention is to maintain the prosthetic joint line as near anatomic aspossible. For example, assuming the above prosthetic dimensions for theGENESIS II femoral prosthesis 198, 8 mm must be resected from the medialtibial condyle or 11 mm from the lateral tibial condyle. This will givea 9.5 mm resection at the midpoint at 0°. With the tibial insert of 9.5mm replaced, the joint level will be elevated 1.5 mm medially andlowered 1.5 mm laterally, but the patellofemoral joint level will benear anatomic. It follows then that 11 mm from the medial femoralcondyle and 8 mm from the lateral femoral condyle (both distally andposteriorly) must be resected to achieve the desired 19 mm bonyresection to accommodate the 19 mm dimensions of the prostheticimplants.

The surgeon must decide whether to resect the thickness of the combinedtibial-femoral prosthesis (i.e., 19 mm) from either the medial orlateral side of the femur 1. The most intact side, least affected or theconvex side should be chosen.

When calculating the amount to be resected for the convex side, thesurgeon should include an estimate of the “millimeters” of convexligament laxity. Otherwise, a too thick tibial prosthesis may benecessary.

Normally the distal femoral resection guide i.e., the lower half 208 oftool 30D (FIG. 21) will contact the medial femoral condyle and beapproximately 3 mm off the lateral femoral condyle. In this situation,11 mm would be resected from the medial femoral condyle. If the knee isin varus and the distal femoral resection guide contacts the lateralfemoral condyle, only 8 mm of bone from the lateral femoral condyle mustbe excised. Therefore, the medial side must be under-resected by 3 mm.Any measurements between these extremes can be easily calculated.

Resecting more than 8 mm medially or 11 mm laterally from the tibialplateau (proximal tibia) may detach or significantly weaken theposterior cruciate ligament (“PCL”) insertion more than is compatiblewith useful function. A tibial plateau that compensates for a lost PCLmay be necessary. Also, lowering the tibial resection may place thetibial prosthesis on to a less supportive cancellous surface.

It is important to achieve proper ligament balancing and not equalflexion-extension spacing. The “normal” knee is stable in full extensionand has some laxity in flexion. A surgeon should allow an extra 2-3 mmof laxity in flexion to accommodate the normal laxity. If the knee hasfull unhindered motion, resection in flexion and extension are equal. Ifflexion is limited, however, an extra few mm in flexion must beresected. (See “Loss of Flexion” situation described below).

A 1 mm resection is approximately equal to 5° increased motion in bothflexion and extension. Although this varies slightly from smallerpatients to larger patients, the results are relatively consistent. Thisalso implies that if the femur 1 is under-resected distally by 1 mm orover-resected posteriorly by 1 mm, 5° extra flexion should be achieved.

When checking range of motion before closing, at least 10° of laxity isrequired in flexion and extension. When arthroscoping a knee, initiallythe joint is quite snug. After “wrestling” with the knee for 5-10minutes, the joint seems to “loosen up”. This can be attributed to“stretching” the ligamentous structures around the knee. There is nonormally organized elastin or reticulin in the soft tissues surroundingthe,knee, but these structures are capable of approximately lengtheningby approximately 10% before failure (i.e., loss of elastic deformationand recovery). Generally, this is approximately 2 mm, which translatesto approximately 10° of motion lost after closure.

Any varus or valgus malalignment must be compensated by removal ofosteophytes and by appropriate medial or lateral ligament and softtissue release, (i.e., concave balancing). Flexion and extensiondeformities are managed with a combination of bony resection, softtissue release, and possibly posterior cruciate release.

The placement of the tibial plateau is also important. Aside fromestablishing proper rotation, posterior placement of the tibial plateaumay be useful to:

1) compensate for shortening of the femur by allowing the tibia to moveposteriorly under the femur;

2) decrease posterior impingement and rollback;

3) decrease posteromedial tibial wear;

4) decrease posterior soft tissue impingement;

5) allow for maintenance of the posterior cruciate ligament if the femuris shortened only a few millimeters; and

6) decrease patellofemoral pressure by anteriorly placing the tibialtubercle relative to the femur.

If the femur 1 is shortened more than approximately 4 mm from“anatomic,” a surgeon should consider releasing the posterior cruciateligament to allow the tibial prosthesis to fall back under the femoralprosthesis in flexion. In addition, releasing the posterior cruciateligament allows increased laxity in flexion. Generally, up to about 3-7mm of extra space can be achieved in flexion and 0-2 mm in extension.

If the posterior cruciate ligament is left intact, flexion often causesposterior impingement (i.e. the “kinetic conflict”). The PCL must bereleased if:

1) There is significant deformity (varus, valgus, flexion, extension).

2) It has become significantly contracted.

3) There has been a patellectomy.

4) The jointline is elevated and/or the femur shortened greater than orequal to 4 mm.

5) The patient has an inflammatory arthritis.

6) Flexion under anesthesia is less than 115°.

If the knee is unstable in flexion, consider under-resection of theproximal tibia. A thicker plastic insert can also be inserted to make upfor the laxity.

If the collateral ligaments are compromised, a more constrained knee maybe indicated. Care must be taken not to create a patella infera. If thisis of concern, then one must pre-operatively determine the propercombination of under-resection of the femur and/or under-resection ofthe tibia.

If the knee is stable in flexion or lacks full flexion, the distal femurshould be under-resected 1 mm for every 5° of desired motion. If theknee is still too tight, more can be resected after trialing. If theflexion space is too loose after resection, then a slightly thickerplastic insert can be inserted with a corresponding loss of flexion.

Preferably, the instrumentation system of the present invention shouldcorrespond to the protocol described below.

The following standard protocol can be followed if a simple procedure isdesired.

Standard Protocol

Resect proximal tibia. Measure from most intact or convex side (leastaffected)

Evaluate and “replace” for asymmetric loss of bone from the posteriorcondyles

Measure AP size

Resect distal femur

Downsize femur and resect condyles and chamfers

Maintain PCL

Resect posterior osteophytes

If the knee lacks 0°-15° extension and 115°—full flexion, then:

1. Resect proximal tibia at standard

2. Measure AP and downsize to next smaller size

3. Resect distal femur≦3 mm extra as needed

4. Leave PCL and resect posterior osteophytes

5. Downsize to next smaller femur

6. If tight in flexion, release PCL and ream for PCL substitution

A more advanced protocol for more specific knee conditions is describedbelow.

Advanced Protocol

“Solving” the Flexion Space

In order to get “full” (i.e., 130°) flexion, the surgeon must balancethe size of the prosthesis, bony resection, soft tissue releasing,proper rotation and proper relationship to the extension space.

If the parameter of PCL release is assumed to be 4 mm, wherein 1 mm boneresection results in 5° gain of motion, then an adequate flexion spacewith an “anatomic” 2-3 mm laxity is easily produced.

The following situations maintain the jointline between 3 mm distallyand or 4 mm proximally starting with flexion from 90°-130° and extensionfrom 55°-0°. The above measurements and parameters will allow for aresultant range of motion of 0°-130° in most patients.

Initial Observations Re: Measurement Variations

As the radius of curvature of the prosthetic condyles increase, theamount of motion gained from:

a. 1 mm bony resection

b. PCL release

c. Posterior capsular release decreases as the radius of curvature ofthe prosthetic condyles increase, i.e., increased size of the distalfemur.

PCL Resection

This procedure generally produces about 3-7 mm of flexion space laxity,which seems to be in inverse relationship to the AP size of the distalfemur (i.e., size 8=3 mm laxity, size 4-5=4 mm laxity, size 2-3=5-6 mm.In the present example, the “gained” space is determined to be 4 mm.

1 mm Resection=5° Gained Motion

It has been found that 1 mm resection allows 3°-6° of increased motionwhich also appears to be in inverse relationship to the AP size of. thedistal femur. This is similar to the motion gained with PCL release.

Therefore, for simplicity, 4 mm of gained space for PCL resection and5°/1 mm bone resection has been allowed in the present example. If themotion range is still tight at the end of the procedure, it would be asimple matter to resect an extra 1-2 mm from proximal tibia.

Varus or Valgus Deformity

Before measuring flexion or extension loss, release the contractedmedial or lateral ligments.

0°-15° Lack of Extension and 95°-105° Flexion

1. Resect proximal tibia at standard

2. Measure, AP, femoral size

3. Under-resect distal femur 3 mm

4. Downsize to next smaller femur—Resect only posterior condyles now.

5. Release the PCL

6. Release posterior capsule as needed

7. Re-resect tibia≦3 mm as needed if tight in flexion

8. Check flexion and extension spaces. Make sure the flexion space isample and that extension is stable at 0°-10° hyperextension.

9. Resect distal femur as needed

10. Resect posterior and anterior condyle

11. Ream for PCL substitution and resect chamfer

15°-25° Lack of Extension and Full Flexion

1. Resect tibia as needed

2. Measure AP femoral size

3. Resect distal femur per standard

4. Upsize to next larger femur

5. Release PCL

6. Release posterior capsule and osteophytes

7. Measure extension space and re-resect distal femur as necessary

8. Resect anterior and posterior condyles

9. Ream for PCL substitution and resect chamfers

15°-25° Lack of Extension and 115°-120° Flexion

1. Resect tibia as indicated

2. Measure AP femoral size

3. Resect distal femur per standard

4. Downsize to next smaller femur

5. Release PCL

6. Resect anterior and posterior condyles

7. Release posterior capsule and osteophytes

8. Measure extension space with blocks

9. Re-resect distal femur as necessary

10. Ream for PCL substitution and resect chamfers

15°-25° Lack of Extension and 95°-115° Flexion

1. Resect tibia as indicated

2. Measure AP femoral size

3. Under-resect distal femur 3 mm

4. Downsize to next smaller femur

5. Release PCL

6. Resect posterior condyles

7. Release posterior capsule and osteophytes

8. Measure extension space with blocks

9. Re-resect proximal tibia as needed

10. Re-resect proximal distal femur as needed

11. Ream for PCL substitution and resect chamfers

25°-40° Lack of Extension>120° Flexion

1. Resect tibia as indicated

2. Measure distal femoral AP size

3. Resect distal femur as standard

4. Upsize to next larger femur

5. Resect posterior condyles

6. Release posterior capsule PCL and osteophytes

7. Measure extension space with blocks

8. If full extension not achieved, over-resect distal femur≦3 mm and/orproximal tibia as needed

9. Complete resection of anterior condyles

10. Ream for PCL substitution and resect chamfers

25°-40° Lack of Extension and 105°-115° Flexion

1. Standard resection of tibia

2. Standard resection of distal femur

3. Measure AP size of femur

4. Downsize to next smaller femur

5. Resect posterior condyles

6. Release posterior capsule PCL

7. Measure extension with spacer block

8. Re-resect distal femur≦3 mm if full extension not achieved and/orproximal tibia as needed

9. Re-resect posterior and anterior condyles, if needed

10. Ream for PCL substitution and resect chamfers

25°-40° Lack of Extension and 90°-105° Flexion

1. Resect tibia<3 mm as needed (choose amount as needed to accommodateflexion or extension)

2. Measure AP size of femur

3. Resect distal femur as standard

4. Downsize to next smaller femur and resect posterior condyles

5. Release PCL

6. Release posterior capsule

7. Check flexion-extension space with blocks

8. Re-resect distal femur<3 mm if full extension not achieved

9. Complete resection of anterior and posterior condyles

10. Ream for PCL substitution and resect chamfers

40°-55° Lack of Extension and Full Flexion

1. Resect tibia as needed

2. Measure AP size of femur

3. Resect distal femur as standard

4. Upsize to next larger femur

5. Resect posterior condyles

6. Release posterior capsule PCL and osteophytes

7. Measure extension with spacer block

8. Resect≦4 mm if from distal femur if needed

9.

a. If full extension, resect anterior condyles and proceed

b. If still not extending, and soft tissue has been released, re-resectproximal tibia 3≦mm. Then complete resection of anterior and posteriorcondyles

10. Ream for PCL substitution and resect chamfers

40°-55° Lack of Extension and 115°-120° Flexion

1. Resect tibia as indicated

2. Measure distal femoral AP size

3. Over-resect distal femur 4 mm

4. Downsize to next smaller femur

5. Resect posterior condyles

6. Release posterior capsule PCL and osteophytes

7. Measure extension with spacer block

8. If still not extending and soft tissue has been released, re-resectProximal tibia≦3 mm

9. Ream for PCL substitution and resect chamfers and anterior condyles

40°-55° Lack of Extension and 105°-115° Flexion

1. Resect proximal tibia

2. Measure AP size of femur

3. Resect distal femur at standard

4. Downsize to next smaller femur

5. Resect posterior condyles

6. Resect PCL and release posterior capsule

7. Measure extension and flexion space with spacer block

8.

a. Re-resect proximal tibia≦3 mm if tight in both flexion and extension.

Then re-resect distal femur≦4 mm if still not extended.

b. If flexion ok and lack full extension, re-resect distal femur≦4 mm

9. Complete resection of anterior and posterior condyles

10. Ream for PCL substitution and complete chamfers

40°-55° of Extension and 90°-105° Flexion

1. Resect proximal tibia plus≦3 mm extra resection as needed

2. Measure AP size of femur

3. Resect distal femur at standard minus overresection of tibia.

4. Downsize to next smaller femur

5. Resect posterior condyles

6. Resect PCL

7. Release posterior capsule and resect osteophytes

8. Measure flexion-extension space with spacer block

9. Re-resect distal femur as necessary

10. Complete resection of anterior and posterior condyles

11. Ream for PCL substitution and complete chamfers

Hyperextension Deformity

1.

 If the knee is unstable in flexion, consider under-resecting theproximal tibia. A thicker plastic insert can also be inserted to make upfor the laxity.

 If the collateral ligaments are compromised, a more constrained kneemay be indicated.

 Care must be taken not to create a patella infera. If this is ofconcern, then one must pre-operatively determine the proper combinationof under-resection of the femur and/or under-resection of the tibia.

2. If the knee is stable in flexion or lacks full flexion, under-resectthe distal femur 1 mm per 5°. If too tight, more can be resected aftertrialing. If too loose, then a slightly thicker plastic insert can beinserted with a corresponding loss of flexion.

3. If there is and initial hyperextension deformity, leave the knee inneutral at the end and not in 10° hyperextension.

Varus or Valgus Laxity

Pre-operative assessment of medial or lateral laxity is important. If onstanding films one can ascertain excess laxity on the convex side of theknee, then appropriate compensation must be made.

1. If there is full flexion, then under-resect the distal femur 2-3 mm

2. If there is a lack of full flexion, under-resect the distal femur 2-3mm and consider releasing the PCL

If there is significant instability, consider a more constrained knee.

It should be realized that to achieve better results with total kneereplacement, orthopedic surgeons must:

1) have accurate measurements;

2) have coordinated measurements;

3) maintain an “anatomic” joint line;

4) have access to dimensions of components; and

5) have the ability to compensate for deformities with a minimum of softtissue release and bony resection.

Although the invention has been described with reference to specificembodiments thereof, it will become apparent to those skilled in the artthat numerous modifications and variations can be made within the scopeand spirit of the invention as defined in the attached claims.

What I claim is:
 1. An apparatus for the placement of a patellar insert,comprising: a patellar clamp for securing a patella to be fitted with apatellar insert, the patellar clamp including a base plate; an armsupported above the base plate; and a collet pivotally secured to thearm such that the patella can be clamped between the base plate and thecollet; and a reamer for reaming away a sufficient amount of patella toaccommodate the patellar insert, the reamer including a depth scale toindicate a depth which has been reamed by the reamer.
 2. The apparatusof claim 1, wherein the depth scale includes markings corresponding to athickness of the patellar insert.
 3. The apparatus of claim 1, whereinthe patellar clamp for securing the patella further comprises, a scaleto indicate a distance between a location at which the prongs intersectthe patella and the baseplate.
 4. The apparatus of claim 1, wherein thecollet includes four prongs on the bottom side thereof.
 5. The apparatusof claim 1, wherein the collet includes a plurality of prongs located ona bottom side thereof which are arranged to be generally equally spacedaround the peak of the patella.